Lamination status inspecting apparatus, lamination status inspecting method, and recording medium storing lamination status detecting program

ABSTRACT

A lamination status inspecting apparatus inspects a lamination status of adjacent sheets, and includes a first illumination unit that irradiates a portion where sheets are adjacent to each other with light from a predetermined direction, a second illumination unit that irradiates with light from a direction opposite to a direction of the first illumination unit, an imaging unit that picks up an image of the portion, and an imaging control unit that controls the imaging unit to pick up a first image of the portion by lighting the first illumination unit, and controls the imaging unit to pick up a second image of the portion by lighting the second illumination unit.

This application is a continuing application, filed under 35 U.S.C. §111(a), of International Application PCT/JP2005/020372, filed Nov. 7,2005, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a compact, lamination status inspectingapparatus, a lamination status inspecting method, and a laminationstatus detecting program for inspecting a lamination status of adjacentsheets.

2. Description of the Related Art

In recent years, a material called prepreg is widely used in fields ofaerospace and sports, in which materials are required to be light-weightand of high performance. Prepreg is a sheet-like, in-process, moldingmaterial in a semi-cured state manufactured by impregnating a carbonfiber with a thermosetting resin. Plural prepreg sheets are unitedtogether to form a multilayer laminate which is then molded throughthermal hardening.

If a prepreg sheet overlaps with an adjacent prepreg sheet during alamination process, or a gap between adjacent prepreg sheets is wide,strength of a finished molded product could be insufficient. Therefore,in the lamination process, it is necessary to check an overlap of theadjacent sheets and an amount of gap therebetween so as to inspect ifthe sheets are properly adhered with each other.

To detect an overlap of adjacent sheets and to measure a gap amount, alevel difference between the sheets needs to be detected. As a techniquefor detecting a level difference, an apparatus is disclosed in JapanesePatent Application Laid-open No. 2001-183113. The disclosed apparatusforms a shade of a step using two illuminations, receives reflectedlights of the illuminations respectively by two sensors utilizingcharacteristic of reflection and transmission of a mirror therebyobtaining two images, and detects a level difference in inspectedobjects based on a difference between the two images.

Conventionally, whether adjacent sheets are properly adhered with eachother is manually inspected. However, this procedure has a problem inthat a person cannot thoroughly inspect the sheets because of theirsignificantly large lamination areas and that the check requires highmanpower cost and time.

Further, the apparatus of Japanese Patent Application Laid-open No.2001-183113 has problems in that the apparatus has a large size becauseof a mirror, two light-receiving sensors, and lenses, and that highprecision is required in positioning of the two light-receiving sensorsbecause of the use of a difference.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partially solve theproblems in the conventional technology.

A lamination status inspecting apparatus according to one aspect of thepresent invention is a lamination status inspecting apparatus thatinspects a lamination status of adjacent sheets, and includes a firstillumination unit that irradiates a portion where sheets are adjacent toeach other with light from a predetermined direction, a secondillumination unit that irradiates with light from a direction oppositeto a direction of the first illumination unit, an imaging unit thatpicks up an image of the portion, and an imaging control unit thatcontrols the imaging unit to pick up a first image of the portion bylighting the first illumination unit, and controls the imaging unit topick up a second image of the portion by lighting the secondillumination unit.

A lamination status inspecting method according to another aspect of thepresent invention is a lamination status inspecting method forinspecting a lamination status of adjacent sheets, and includes firstlypicking up a first image of a portion where sheets are adjacent to eachother by irradiating the portion with light from a predetermineddirection, and secondly picking up a second image of the portion byirradiating the portion with light from a direction opposite to thepredetermined direction.

A computer-readable recording medium according to still another aspectof the present invention is a computer-readable recording medium thatstores therein a computer program that causes a computer to execute alamination status detecting program, and the computer program causes thecomputer execute firstly detecting a sheet end from a first imageobtained by imaging a portion where sheets are adjacent to each other byirradiating the portion with light from a predetermined direction,secondly detecting a sheet end from a second image obtained by imagingthe portion by irradiating the portion with light from a directionopposite to the predetermined direction, and determining a laminationstatus between the sheets based on a detection result in the firstlydetecting and a detection result in the secondly detecting.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a configuration of a laminationstatus inspecting apparatus according to a first embodiment;

FIG. 2A is a front view of an example of a setting of two illuminationdevices and an imaging device of the lamination status inspectingapparatus of the first embodiment;

FIG. 2B is a side view of the example shown in FIG. 2A;

FIG. 2C is a bird's-eye view of the example shown in FIG. 2A;

FIG. 3 is a diagram of an example of a picked-up image when there is agap between sheets;

FIG. 4 is a diagram of an example of a picked-up image when there is nogap between sheets;

FIG. 5 is a diagram of an example of a picked-up image when sheets areoverlapped with each other;

FIG. 6 is a functional block diagram of a configuration of a laminationstatus inspecting apparatus according to a second embodiment;

FIG. 7 is a side view of a lamination status inspecting apparatus whensheets have an inclination;

FIG. 8 is a diagram of an example of a picked-up image when there is agap between inclined sheets;

FIG. 9 is a diagram of an example of a picked-up image when there is nogap between inclined sheets;

FIG. 10 is a diagram of an example of a picked-up image when there is anoverlap of inclined sheets;

FIG. 11 is a flowchart of a process procedure of a lamination statusdetecting process performed by an image processing device;

FIG. 12 is a flowchart of a process procedure of a sheet-end detectingprocess performed by a sheet end detector;

FIG. 13 is an example of coefficients of an edge enhancement filter;

FIG. 14 is a diagram of an example of coefficients of an edge detectionfilter used for one picked-up image;

FIG. 15 is a diagram of an example of coefficients of an edge detectionfilter used for another picked-up image; and

FIG. 16 is a functional block diagram of a configuration of a computerexecuting a lamination status detecting program according to the secondembodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of a lamination status inspecting apparatus, alamination status inspecting method, and a lamination status detectingprogram according to the present invention will be explained below indetail with reference to the accompanying drawings. Note that theinvention is not limited to the embodiments.

First, a configuration of a lamination status inspecting apparatusaccording to a first embodiment is explained. FIG. 1 is a functionalblock diagram of a configuration of a lamination status inspectingapparatus according to the first embodiment. As shown in FIG. 1, alamination status inspecting apparatus 100 includes an illuminationdevice 1, an illumination device 2, an imaging device 3, and an imagingcontrol device 4, an illumination control device 5, and an image displaydevice 6.

The illumination device 1 irradiates with light a portion where a sheet,which is just applied as a laminate, comes next to an adjacent sheetwhich is adjacent to the just-applied sheet. The illumination device 2irradiates the portion where the just-applied sheet comes next to theadjacent sheet with light from a direction opposite to a direction ofthe light from the illumination device 1. As light emitting elements ofthe illumination device 1 and the illumination device 2, elements suchas LEDs having a short rising time till light emission are used toswitch over the illuminations.

The imaging device 3 picks up an image of a portion where thejust-applied sheet comes next to the adjacent sheet. A CCD or a CMOS isused as an imaging element. Regarding a size of the imaging element, thenumber of pixels, a frame rate, a scan system, a lens, and an opticalfilter, optimum ones are selected depending on an inspection target andinspection performance.

FIGS. 2A, 2B, and 2C are views of an example of a setting of theillumination device 1, the illumination device 2, and the imaging device3, and are a front view, a side view, and a bird's-eye view,respectively. As shown in FIGS. 2A, 2B, and 2C, the imaging device 3 isarranged substantially perpendicularly to the sheets, above the sheetend.

The illumination device 1 is arranged so that an angle formed betweenthe light axis of the illumination device 1 and the sheets is θ1, and anangle between the light axis and the sheet end is Φ1, as shown in FIGS.2A, 2B, and 2C. Here, θ1 is properly determined based on the thicknessof the sheet, the number of pixels of the imaging device 3, a type oflens, and a distance between the imaging device and the sheets. Thoughit is desirable that Φ1 be zero, a tolerable range of Φ1 is setapproximately to ±5° depending on the position of arrangement.

The illumination device 2 is arranged so that an angle formed betweenthe light axis of the illumination device 2 and the sheets is θ2, and anangle between the light axis and the sheet end is Φ2, as shown in FIGS.2A, 2B, and 2C. Here, θ2 and Φ2 are determined in a similar manner tothat of θ1 and Φ1, and θ2=θ1 and Φ2=Φ1.

The imaging control device 4 controls imaging, for example, bycontrolling a shutter timing of the imaging device 3, a shutter releasetime, and gain. The imaging control device 4 instructs the illuminationcontrol device 5 so that the lighting of the illumination device 1 andthe illumination device 2 and the shutter timing of the imaging device 3are synchronous.

That is, the imaging control device 4 instructs the illumination controldevice 5 to alternately light the illumination device 1 and theillumination device 2, and also instructs the imaging device 3 to pickup an image when each illumination device is lighted. An image that theimaging device 3 picks up when the illumination device 1 is lighted iscalled a picked-up image₁, and an image that the imaging device 3 picksup when the illumination device 2 is lighted is called a picked-upimage₂.

When the imaging control device 4 instructs the illumination controldevice 5 to alternately light the illumination device 1 and theillumination device 2, and also instructs the imaging device 3 to pickup an image when each illumination device is lighted, the single imagingdevice 3 is sufficient for picking up images formed by pluralilluminations.

The illumination control device 5 controls lighting, for example, bycontrolling a lighting timing and a lighting time of the illuminationdevice 1 and the illumination device 2 based on the instructions of theimaging control device 4. While the imaging control device 4synchronizes the lighting of each illumination device and the imaging bythe imaging device 3 in this example, the illumination control device 5can synchronize the lighting of each illumination device and the imagingby the imaging device 3, and instructs the imaging timing to the imagingcontrol device 4.

The illumination device 1 and the illumination device 2 are switchedfrom one to another so as to alternately light up each n (n≧1) frames.When the imaging device of the interlace system is used, the lightingcan be changed over for each field. In this case, even fields and oddfields are irradiated with different illuminations. When the lightemitting elements that can perform pulse lighting such as an LED areemployed, the light emitting timing and the light emitting time of thelight emitting element are matched with the release timing and releasetime of the shutter of the imaging element, so as to realize efficientlighting.

The image display device 6 takes in image signals output from theimaging control device 4, and displays an image on a display. A devicehaving a display function such as a personal computer or a televisionhaving an external input function is used for the image display device6. The image display device 6 can directly display images by switchingthe images for each frame or each field, and can display two imagesseparately as the illumination device 1 and the illumination device 2are lighted.

Examples of the picked-up image₁ obtained by the imaging device 3 whenthe illumination device 1 is lighted and the picked-up image₂ obtainedby the imaging device 3 when the illumination device 2 is lighted areexplained with reference to FIG. 3 to FIG. 5. FIG. 3 is a diagram of anexample of a picked-up image when there is a gap between sheets. Asshown in FIG. 3, in the picked-up image₁ a step between the just-appliedsheet and a lower-layer sheet appears as a shade, and the left side ofthe shade is an end of the just-applied sheet. Similarly, in thepicked-up image₂, a step between the adjacent sheet and the lower-layersheet appears as a shade, and the right side of the shade is an end ofthe adjacent sheet. When the gap between the just-applied sheet and theadjacent sheet is accommodated within a screen, the sheet end can beconfirmed in both images as shown in FIG. 3.

For the screen shown in FIG. 3, an origin of the coordinates of thescreen is set to an upper left point as (x, y)=(0, 0). A position of thesheet end is represented by the x-coordinate. Specifically, a positionof the sheet end detected in the picked-up image₁ is expressed by itsx-coordinate x₁, and a position of the sheet end detected in thepicked-up image₂ is expressed by its x-coordinate x₂.

FIG. 4 is a diagram of an example of a picked-up image when there is nogap between the sheets. As shown in FIG. 4, when there is no gap betweenthe sheets, the sheet end cannot be confirmed in either one of theimages.

FIG. 5 is a diagram of an example of a picked-up image when sheets areoverlapped with each other. As shown in FIG. 5, when the just-appliedsheet extends over the adjacent sheet, a step appears as a shade in thepicked-up image₁, and no shade can be confirmed in the picked-up image₂.When there is no adjacent sheet or when a gap between the just-appliedsheet and the adjacent sheet cannot be accommodated in the screen, ashade sometimes cannot be confirmed in the picked-up image₂ similarly tothe example shown in FIG. 5.

As described above, in the first embodiment, the imaging control device4 controls so that the imaging device 3 picks up an image of a portionwhere the just-applied sheet lies side by side with the adjacent sheet,by irradiating the portion alternately with the light from theillumination device 1 and the light from the illumination device 2.Therefore, a compact device can inspect the lamination status of thesheets without using a mirror, two light-receiving sensors, and twolenses.

While the first embodiment explains the case where the image displaydevice 6 displays the images picked up by the imaging device 3, alamination status of sheets can be also automatically determined byprocessing the images picked up by the imaging device 3. A secondembodiment explains a lamination status inspecting device thatautomatically determines a lamination status of sheets by processing theimages picked up by the imaging device 3.

Firstly, a configuration of the lamination status inspecting deviceaccording to the second embodiment is explained. FIG. 6 is a functionalblock diagram of a configuration of the lamination status inspectingapparatus according to the second embodiment. Functional units thatoperate similarly to those of the units in FIG. 1 are denoted by likereference numerals, and detailed explanations thereof will not berepeated for the convenience of description.

As shown in FIG. 6, a lamination status inspecting device 200 includesthe illumination device 1, the illumination device 2, the imaging device3, the imaging control device 4, the illumination control device 5, andan image processing device 60. The image processing device 60automatically determines a lamination status of sheets by processingimages picked up by the imaging device 3, and includes a sheet enddetector 61, an overlap determining unit 62, and a gap-amount measuringunit 63.

The sheet end detector 61 is a processing unit that detects a sheet endby processing images picked up by the imaging device 3. Specifically,the sheet end detector 61 detects a sheet end, using a shade generatedin the picked-up image₁ and the picked-up image₂ shown in FIG. 3 to FIG.5.

The overlap determining unit 62 is a processing unit that determineswhether there is an overlap or a gap between a just-applied sheet and anadjacent sheet based on a sheet end detected by the sheet end detector61. Specifically, when a sheet end is detected in both the picked-upimage₁ and the picked-up image₂, the overlap determining unit 62determines that there is a gap between the just-applied sheet and theadjacent sheet. When a sheet end is detected in the picked-up image₁ andis not detected in the picked-up image₂, the overlap determining unit 62determines that the just-applied sheet is overlapped with the adjacentsheet. When a sheet end is not detected from any of the picked-up image₁and the picked-up image₂, the overlap determining unit 62 determinesthat the just-applied sheet lies next to the adjacent sheet without agap.

The gap-amount measuring unit 63 is a processing unit that calculates agap amount when the overlap determining unit 62 determines that there isa gap between the just-applied sheet and the adjacent sheet.Specifically, the gap-amount measuring unit 63 calculates a differencebetween x₂ and x₁ shown in FIG. 3 as a gap amount.

In the above, the sheet end detector 61 detects a sheet end using shadesshown in FIG. 3 to FIG. 5. However, a sheet end cannot be detected usinga shade in some cases. A method of detecting a sheet end when a sheetend cannot be detected using a shade is explained next.

Assume that a laminate sheet is a carbon sheet. The carbon sheet has acharacteristic that when the sheet is irradiated with light from adirection perpendicular to a fiber direction, reflection of the light isstrong, and that when the sheet is irradiated with light from the samedirection as the fiber direction, reflection of the light is weak. Sincethe sheets are arranged in the fiber direction in lamination, indetecting an overlap or a gap between sheets to be inspected, it issufficient if the sheet is always irradiated with light from a directionperpendicular to the fiber direction. In this case, a contrast betweenthe shade portion and other sheet portion is strong. Therefore, a sheetend can be detected easily. In some cases, an entire portion of the gaphas a significantly low brightness because of a difference of fiberdirection of the laminate sheet and the adjacent sheet, and the gapcannot be distinguished from a shade. Even in such case, if a method ofdetecting an edge is used, the gap can be detected by the same detectingmethod as that of detecting only a shade.

However, a lamination device often laminates sheets in dozens of layersand hundreds of layers, and inspected sheets are sometimes dozens ofmeters in size. Therefore, when a device independent of the laminationdevice performs inspections alone, a very long time is required.Further, if the inspection is performed by a device independent from thelamination device, a structure must be formed so that the laminationstatus inspecting apparatus and the inspected object can be transportedduring a sheet lamination process of the inspected objects for themeasurement of an overlap and a gap amount of adjacent sheets, which isvery inefficient. Accordingly, it is necessary to fit the laminationstatus inspecting apparatus to the lamination device to eliminate theneed of taking time for the inspection in addition to the time forlamination by simultaneously performing lamination and inspection.

However, when the lamination status inspecting apparatus is fitted tothe lamination device, there is a drawback in that the sheet to bedetected, the illuminations, and the camera cannot be always held in aconstant positional relationship. The lamination device laminates sheetswith a roller, and therefore can laminate the sheets without incliningthe axis when laminating sheets on the lamination surface of an upwardslope or a downward slope. Therefore, unless the lamination statusinspecting apparatus has a system that can constantly keep the sheets,the illuminations, and the camera in a predetermined positionalrelationship following the upward slope or the downward slope, thesheets can be inclined relative to the imaging device and theillumination device as shown in FIG. 7.

When the sheets are inclined as described above, the following changesoccur in the image picked up by the imaging device.

(1) Because an angle formed between the fiber direction of the sheet andthe illumination direction is not a right angle, brightness of the sheetlowers as the inclination angle increases.

(2) Because a step in the sheets is irradiated by illuminations,reflection from the step is stronger than that from other portions.Therefore, brightness is kept high even when the sheets are inclined.

Because of (1) and (2), when the sheets are inclined, an image havinghigh brightness only in a step portion is obtained, as shown in FIG. 8to FIG. 10. FIG. 8 is a diagram of an example of a picked-up image whenthere is a gap between inclined sheets. FIG. 9 is a diagram of anexample of a picked-up image when there is no gap between inclinedsheets. FIG. 10 is a diagram of an example of a picked-up image whenthere is an overlap of inclined sheets.

When sheets are inclined, edges obtained from the picked-up image₁ andthe picked-up image₂ are at opposite positions from those detected basedon the shades. Specifically, the sheet end detector 61 detects the sheetend x₂ from the picked-up image₁ and detects the sheet end x₁ from thepicked-up image₂.

When only the step portion has high brightness, an inclination angle αdepends on a size of and a distance from the illumination. When theillumination is made larger or is brought nearer, the inclination angleα becomes larger, whereas when the illumination is made smaller or isbrought farther, the inclination angle α becomes smaller.

In FIG. 7, the brightness of the sheets becomes gradually lower when theinclination angle α becomes large. Therefore, it is possible to fit thelamination status inspecting apparatus to the lamination device so thatthe imaged sheets is always in a same fiber direction within apredetermined region (hereinafter referred to as “region S”) of apicked-up image, and to switch a manner of detection between two mannersdepending on an average brightness of the region S: according to onemanner, the detection is performed utilizing the shade generated in astep portion; according to another manner, the detection is performedutilizing the fact that the brightness increases only in the stepportion.

Specifically, when average brightness of the region S is equal to orhigher than a threshold value, the sheet end x₁ is detected using thepicked-up image, and the sheet end x₂ is detected using the picked-upimage₂. On the other hand, when average brightness of the region S isnot equal to or higher than a threshold value, the sheet end x₂ isdetected using the picked-up image, and the sheet end x₁ is detectedusing the picked-up image₂.

A process procedure of the lamination status detecting process performedby the image processing device 60 is explained next. FIG. 11 is aflowchart of a process procedure of the lamination status detectingprocess performed by the image processing device 60. This laminationstatus detecting process is performed each time the picked-up image₁ andthe picked-up image₂ are taken in.

As shown in FIG. 11, the overlap determining unit 62 of the imageprocessing device 60 determines whether the average brightness of theregion S is equal to or higher than a threshold value (step S101). Whenthe average brightness of the region S is equal to or higher than thethreshold value, the sheet end detector 61 detects the sheet end x₁ inthe picked-up image₁ (step S102), and detects the sheet end x₂ in thepicked-up image₂ (step S103). On the other hand, when the averagebrightness of the region S is lower than the threshold value, the sheetend detector 61 detects the sheet end x₂ in the picked-up image₁ (stepS104), and detects the sheet end x₁ in the picked-up image₂ (step S105).

The overlap determining unit 62 determines whether the sheet end x₁ isdetected (step S106). When the sheet end x₁ is detected, the overlapdetermining unit 62 determines whether the sheet end x₂ is detected(step S107). When the sheet end x₂ is not detected as a result, thesheets are overlapped with each other. Therefore, a result of thedetermination is set as “overlapped” (result=LAP) (step S108).

On the other hand, when the sheet end x₂ is detected, the gap-amountmeasuring unit 63 calculates a gap amount (gap) using a differencebetween x₂ and x₁ (step S109). When a lateral width of an imaging rangeof the imaging device 3 is w [mm], and the number of pixels in thelateral direction of the image is represented as “width”,gap=(x₂−x₁)*p=(x₂−x₁)*w/width.

The overlap determining unit 62 determines whether the gap amount isequal to or larger than 0.0 mm (step S10). When the gap amount is equalto or larger than 0.0 mm, a gap is present between the sheets.Therefore, a result of determination is set to “there is gap”(result=GAP) (step S111). When the gap amount is smaller than 0.0 mm,there is an abnormality in the detection of the sheet end. Therefore, aresult of determination is set to “error” (result=ERR) (step S113).

When the sheet end x₁ is not detected, the overlap determining unit 62determines whether the sheet end x₂ is detected (step S112). When thesheet end x₂ is detected, the just-applied sheet is not beneath theadjacent sheet, and the sheet end is not properly detected. Therefore, aresult of determination is set to “error” (result=ERR) (step S113). Whenthe sheet end x₂ is not detected, there is no gap between the sheets.Therefore, the gap amount is set to 0.0 mm (step S114), and a result ofdetermination is set to “there is gap” (result=GAP) (step S115).

As explained above, since the overlap determining unit 62 determines agap and an overlap between the sheets based on a result of the sheet enddetection by the sheet end detector 61, a lamination status of thesheets can be inspected.

Next, a process procedure of a sheet-end detecting process performed bythe sheet end detector 61 is explained. FIG. 12 is a flowchart of aprocess procedure of the sheet-end detecting process performed by thesheet end detector 61. As shown in FIG. 12, the sheet end detector 61applies an edge enhancement filter to a picked-up image (step S201).

The edge enhancement filter is a filter of coefficients as shown in FIG.13, for example. When a pixel concerned is f(x, y), a pixel value g(x,y) after the edge enhancement filter is applied can be represented bythe following equation (1).

$\begin{matrix}{{g\left( {x,y} \right)} = {\sum\limits_{i = {x - 1}}^{x + 1}\;{\sum\limits_{j = {y - 1}}^{y + 1}\;{k_{i,j}*{f\left( {i,j} \right)}}}}} & (1)\end{matrix}$

An edge detection filter is applied to the image to which the edgeenhancement filter is applied (step S202). For the picked-up image₁ theedge detection filter is a filter of coefficients as shown in FIG. 14,for example, and for the picked-up image₂, the edge detection filter isa filter of coefficients as shown in FIG. 15, for example.

The image to which the edge detection filter is applied is binarized(step S203). A predetermined threshold value can be used for thebinarization. Alternatively, a gradation histogram can be generated, anda threshold value may be set to a gradation value of higher 5% of atotal number of pixels of an image so that the threshold value isvariable. When the threshold value is th, and a pixel concerned is f(x,y), a binarized pixel value g(x, y) can be represented by the followingequation (2).

$\begin{matrix}{{g\left( {x,y} \right)} = \left\{ \begin{matrix}{1\left( {{{when}\mspace{14mu}{f\left( {x,y} \right)}} \geq {th}} \right)} \\{0\left( {{except}\mspace{14mu}{above}} \right)}\end{matrix} \right.} & (2)\end{matrix}$

The binarized image is projected in a perpendicular direction (stepS204), and a histogram is generated. When the binarized pixel value isf(x, y), a histogram h(x) is obtained by the following equation (3),where “height” is the number of pixels in a vertical direction of theimage.

$\begin{matrix}{{h(x)} = {\sum\limits_{y = 0}^{{height} - 1}\;{f\left( {x,y} \right)}}} & (3)\end{matrix}$

Lastly, the sheet end positions x₁ and x₂ are calculated using thehistogram h(x) (step S205). In calculating the position x₁ of the sheetend in the picked-up image₁, the value of h(x) is checked starting fromx=0 in an ascending order, and when h(x) shows a peak value equal to orhigher than a predetermined threshold value for the first time, acorresponding “x” is set as the position x1 of the sheet end. Incalculating the position x₂ of the sheet end in the picked-up image₂,the value of h(x) is checked starting from x=width−1 (where widthrepresents the number of pixels in the lateral direction) in adescending order, and when h(x) shows a peak value equal to or higherthan a predetermined threshold value for the first time, a corresponding“x” is set as the position x2 of the sheet end.

In calculating the position x₂ of the sheet end in the picked-up image₁,filter coefficients shown in FIG. 14 are used as the edge detectionfilter, and the value of h(x) is checked starting from x=width−1 in adescending order, and when the value of h(x) takes a peak value equal toor higher than a predetermined threshold value for the first time, acorresponding “x” is set as the position x₂ of the sheet end. Incalculating the position x₁ of the sheet end in the picked-up image₂,filter coefficients shown in FIG. 15 are used as the edge detectionfilter, and the value of h(x) is checked starting from x=0 in anascending order, and when the value of h(x) takes a peak value equal toor higher than a predetermined threshold value for the first time, acorresponding “x” is set as the position x₁ of the sheet end.

As described above, in the second embodiment, the sheet end detector 61of the image processing device 60 detects a sheet end from the picked-upimage, and the overlap determining unit 62 determines a gap and anoverlap between sheets based on the sheet end detected by the sheet enddetector 61. Thus, a sheet lamination status can be inspected.

In the second embodiment, the overlap determining unit 62 determineswhether the average brightness of the region S of the picked-up image isequal to or higher than a predetermined threshold value. When theaverage brightness of the region S of the picked-up image is not lowerthan a predetermined threshold value, the sheet end is detected based ona fact that the brightness is high only in the step portion of thesheet. Therefore, the sheet end can be detected in high precision evenwhen the sheets are in an inclined state.

In the second embodiment, the image processing device 60 that operatesas a lamination status detecting device detecting a lamination status isexplained. Further, a lamination status detecting program having asimilar function can be also obtained by realizing the configuration ofthe image processing device 60 by software. A computer that executesthis lamination status detecting program is explained next.

FIG. 16 is a functional block diagram of a configuration of a computerexecuting the lamination status detecting program according to thesecond embodiment. As shown in FIG. 16, a computer 300 includes a RAM310, a CPU 320, an HDD 330, a LAN interface 340, an input/outputinterface 350, and a DVD drive 360.

The RAM 310 is a memory storing programs and an intermediate result ofthe execution of a program. The CPU 320 is a central processing unitreading a program from the RAM 310 and executing the program.

The HDD 330 is a disk device storing programs and data. The LANinterface 340 is an interface for connecting the computer 300 to othercomputer via a LAN.

The input/output interface 350 is an interface for connecting an inputunit and a display unit such as a mouse and a keyboard. The DVD drive360 is a device for reading and writing of the DVD.

A lamination status detecting program 311 executed by the computer 300is stored in the DVD. The DVD drive 360 reads the lamination statusdetecting program 311 from the DVD, and installs the read program intothe computer 300.

Alternatively, the lamination status detecting program 311 is stored ina database of other computer system connected via the LAN interface 340,and is read from this database and is installed into the computer 300.

The installed lamination status detecting program 311 is stored in theHDD 330, and is read out to the RAM 310. The CPU 320 executes the readprogram as a lamination status detecting process 321.

In the first embodiment and the second embodiment, inspection of a gapand an overlap between sheets is explained. However, the presentinvention is not limited thereto, and the invention can also besimilarly applied to the inspection of a gap, an overlap, and a leveldifference between objects other than the sheets.

According to the embodiments as described above, no mirror is required,and one light-receiving sensor and one lens are sufficient. Therefore,there is an effect that the lamination status can be inspected with acompact apparatus.

According to the embodiments as described above, an inspection of alamination status can be automated without depending on a manual work.Therefore, there is an effect that inspection precision can be improvedand inspection cost and inspection time can be decreased.

According to the embodiments as described above, a sheet end is detectedeven when the brightness is low. Therefore, there is an effect that alamination status can be determined even when a reflection light fromthe sheet is weak because of, for example, the inclination of the sheet.

As described above, the lamination status inspecting apparatus, thelamination status inspecting method, and the lamination status detectingprogram according to the present invention are useful for manufacturinga molded product by laminating sheets, and are particularly suitablewhen a gap and an overlap between the sheets significantly affect thequality of the molded product.

Although the invention has been described with respect to specificembodiments for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

1. A lamination status inspecting apparatus that inspects a laminationstatus of adjacent sheets, comprising: a first illumination unit thatirradiates a portion where sheets are adjacent to each other with lightfrom a predetermined direction; a second illumination unit thatirradiates with light from a direction opposite to a direction of thefirst illumination unit; an imaging unit that picks up an image of theportion; and an imaging control unit that controls the imaging unit topick up a first image of the portion by lighting the first illuminationunit, and controls the imaging unit to pick up a second image of theportion by lighting the second illumination unit.
 2. The laminationstatus inspecting apparatus according to claim 1, further comprising asheet end detector that detects a sheet end from the first image and thesecond image, and a lamination status determining unit that determines alamination status between the sheets based on a detection result of thesheet end by the sheet end detector.
 3. The lamination status inspectingapparatus according to claim 2, wherein when brightness of an image isequal to or higher than a predetermined threshold value, the sheet enddetector detects the sheet end using a shade generated from a step inthe portion, and when the brightness of the image is lower than thepredetermined threshold value, the sheet end detector detects the sheetend using an image portion having higher brightness than brightness of asurrounding portion when a step is present in the portion.
 4. Alamination status inspecting method for inspecting a lamination statusof adjacent sheets, comprising: firstly picking up a first image of aportion where sheets are adjacent to each other by irradiating theportion with light from a predetermined direction; and secondly pickingup a second image of the portion by irradiating the portion with lightfrom a direction opposite to the predetermined direction.
 5. Thelamination status inspecting method according to claim 4, furthercomprising detecting a sheet end from the first image and the secondimage, and determining a lamination status between the sheets based on adetection result in the detecting.
 6. The lamination status inspectingmethod according to claim 5 wherein in the detecting, the sheet end isdetected using a shade generated from a step in the portion whenbrightness of an image is equal to or higher than a predeterminedthreshold value, and the sheet end is detected using an image portionhaving higher brightness than brightness of a surrounding portion when astep is present in the portion when the brightness of the image is lowerthan the predetermined threshold value.
 7. A computer-readable recordingmedium that stores therein a computer program that causes a computer toexecute a lamination status detecting program, the computer programcausing the computer execute: firstly detecting a sheet end from a firstimage obtained by picking up an image of a portion where sheets areadjacent to each other by irradiating the portion with light from apredetermined direction; secondly detecting a sheet end from a secondimage obtained by picking up an image of the portion by irradiating theportion with light from a direction opposite to the predetermineddirection; and determining a lamination status between the sheets basedon a detection result in the firstly detecting and a detection result inthe secondly detecting.
 8. The computer-readable recording mediumaccording to claim 7, wherein in the firstly and secondly detecting, thesheet end is detected using a shade generated from a step in the portionwhen brightness of an image is equal to or higher than a predeterminedthreshold value, and the sheet end is detected using an image portionhaving higher brightness than brightness of a surrounding portion when astep is present in the portion when the brightness of the image is lowerthan the predetermined threshold value.